In her nine years as a financial planner at Morgan Stanley Dean Witter in Sacramento, Calif., Marilyn White, a onetime schoolteacher, has been educating her clients, many of whom are black, on the best ways to invest for the future.

But Ms. White wasn't ready for a comment she heard at a recent seminar. A black woman stood up and said, " 'I've always been intimidated, fearful, to walk into a brokerage firm, because I thought I...